Characterization of the novel broad-spectrum kinase inhibitor CTx-0294885 as an affinity reagent for mass spectrometry-based kinome profiling

Kinase enrichment utilizing broad-spectrum kinase inhibitors enables the identification of large proportions of the expressed kinome by mass spectrometry. However, the existing inhibitors are still inadequate in covering the entire kinome. Here, we identified a novel bis-anilino pyrimidine, CTx-0294885, exhibiting inhibitory activity against a broad range of kinases in vitro, and further developed it into a Sepharose(R) supported kinase capture reagent. Use of a quantitative proteomics approach confirmed the selectivity of CTx-0294885-bound beads for kinase enrichment. Large-scale CTx-0294885-based affinity purification followed by LC-MS/MS led to the identification of 235 protein kinases from MDA-MB-231 cells, including all members of the AKT family that had not been previously detected by other broad spectrum kinase inhibitors. Addition of CTx-0294885 to a mixture of three kinase inhibitors commonly used for kinase-enrichment increased the number of kinase identifications to 261, representing the largest kinome coverage from a single cell line reported to date. Coupling phosphopeptide enrichment with affinity purification using the four inhibitors enabled the identification of 799 high confidence phosphosites on 183 kinases, approximately 10 of which were localized to the activation loop, and included previously unreported phosphosites on BMP2K, MELK, HIPK2 and PRKDC. Therefore, CTx 0294885 represents a powerful new reagent for analysis of kinome signalling networks that may facilitate development of targeted therapeutic strategies.